Ultrasonic dispersive delay line



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ULTRASONIC DISPERSIVE DELAY LINE .LQ ik@ i, 1957 3 Sheets-Sheet 33,48tt,6tl7 ULTRASIONC DESFIERSIWE DELAY LINE Wayne I.. iongianni, LaHabra, Calif., assigner to Hughes Aircraft Company, Culi/er City,Calif., a corporation of Delaware Filled May d, 1967, Ser. No. 636,@63lint. fCl. Hilh 7/30 ril. S33-3d 2 Claims ESTRACT OF THE DISCLOSURE Theapparatus of the present invention provides an ultrasonic dispersivedelay line that employs a uniformly ruled optical diffraction grating ona media in which ultrasonic waves can be launched from a singletrar1sducer. In operation, the uniform optical diffraction gratingsteers the ultrasonic wave in a direction determined by the frequencythereof so as to produce a path length that is a function of theultrasonic frequency thereby expanding or compressing the microwavesignal in accordance with the acoustic time delay versus frequencycharacteristics of the device. The grating is scribed with a 60 degreecut blazing angle to provide maximum senA` sitivity at a 60 degreediffraction angle. Lenseless focus1 sing is achieved by the use of amedia having a Rowland circle configuration to increase the frequencyrange of operation.

BACKGROUND OF THE INVENTION The device of the present inventionconstitutes an ultrasonic dispersive delay line. One contemporary devicecalled a perpendicular diffraction delay line provides linear frequencymodulation. This delay line consists of two transducer arraysone fortransmitting and the other for receivingdistributed along theperpendicular surfaces of a delay medium. Other contemporary forms ofdispersive delay lines are known as surface wave dispersive delay linesand wedge dispersivedelay lines. All of these contemporary devicescomprise Aan ultrasonic grating illuminated by a nondispersive acousticwave.

SUMMARY OF THE INVENTION ln accordance with a rst embodiment of thepresent invention, an ultrasonic wave is launched in a media from asingle transducer towards an opposing surface on which is scribed auniformly ruled optical diffraction grating. This optical diffractiongrating reflects the ultrasonic wave back towards a receiving tranducerof sub stantial dimensions along a path length that varies with thefrequency of the wave. In an alternate'lembodiment, the surface of themedia on which the uniformly ruled optical diffraction grating isscribed has the configuration of the concave side of a Rowland circle,thereby to cause the reflected ultrasonic Wave to irripinge on thereceiving transducer over a broader range of frequencies.

In that the device of the subject invention does not employ an array oftransducers as is the case with con temporary delay lines of this type,it does not have the concomitant limitations introduced by themechanical 'tolerances of an array. As a consequence, the delay line ofthe present invention has much higher operating frequency and acorrespondingly greater actual band width, eg., the device may beoperated at 30 and 9G rnc/sec. as compared to a center frequency of 1.7mc./ sec. for the contemporary delay lines,

y particular, the device of FIG. 1, shown in a ,y Bassetti Fatented dan.fi, i977 FIGS. 4 and 5 show performance characteristics of the device ofFIG. 1;

FIG. 6 shows a perspective View of a second embodi-A ment of theinvention incorporating a grating scribed on a Rowland circle; and

FIGS. 7 and 8 show schematic diagrams which illusu trate the operationof the device of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 of thedrawings, there is shown a rst embodiment of the delay line of thepresent invention utilizing a scribed refiecting grating on a planarsurface together with adjustable lapped transducers. In cut-a-way View,includes a rectangular quartz block 10 having broad rectangular opposingsurfaces 11, 12 and a conductive layer 14 such as, for example, goldfilm disposed over the entire surface 11. A lucite container 15 supportsthe quartz block 10 around the periphery thereof with no direct contactwith the broad rectangular surfaces 11, 12 except at the edges. Inaddition, the container 15 is spanned by a longitudinal piece of metal16 over the conductive layer 1d.

PZT ceramic transducers 17, 18, 19 20 are pressed against the conductivelayer 14 of block 10 utilizing adjusting screw mechanisms 21, 22, 23,24, respectively. The PZT ceramic transducers 17, 13, 19, 20are,connected to the center conductors 25, 26, 27, 28 respec* tively, ofcoaxial connectors 29, 30, 31 32 which are disposed lengthwise along thelongitudinal piece of metal 16 over the transducer 17, 18, 19 or 20corresponding thereto and with the respective outer conductors thereofconnected thereto. The longitudinal piece of metal is, in turn,connected to the conductive layer 14 by means of a metallic strip 33.

A scribed reecting grating 35 is disposed normal to the longitudinalpiece of metal 16 on the side 11 of rectangular quartz block 10 oppositethe transducers 17, 18, 19, 20. The grating 35 is scribed at 80 linesper cen timeter and a cutblazing angle of 60 degrees to provide maximumsensitivity at the 60 degree diffraction angle which corresponds ,to afrequency of megacycles.

Referring to FIG. 2 there is geometry for the singleended operationconfiguration for the device of FIG. 1. The grating equation for thefirst order is:

d(sin --sin t (l) where d is the distance between ruled lines, 0 is thedif* fraction angle, z' is the incident angle, and )t is the wavelength.The single-ended operation conguration is the simplest mode of operationand involves selecting one of the transducers 17, 18 1.9 or 20 oppositethe grating 3S. In this mode of operation, the output signals are takenfrom the same transducer to which the input signals are applied.Dispersed signals are generated when the input transducer aperture widthis made equal to or less than a predetermined width, D. For a frequencyof 25 megacycles/sec. and a transducer grating range, R, of 2.54 cm.

DST/gr-"ILN cm.

The selected transducer 17, 18, 19 or 20 will receive the diii'ractedoutput wave for =0 whereby the diffraction Equation 1 becomes: t

2d sin 0:1 (2) Since a=VL/f where VL is the velocity of the longsananetsin 6: w 0l From fFlG. 2, the distance traveled by the ultrasonic 'waveis:

cos 0 From quations 3 and 4, the time, t, for the longitudinai wave totravel the distance 2r is:

"Wifi The actual dispersion resulting from the single-ended A .mode ofoperation of the device of FlG. i is illustrated by the characteristic36, FIG. 4, together with the theoretical dispersion calculated fromEquation 5 illustrated by characteristic 37. it is evident that thetheoretical values of time delay are greater than the actual valuesshown by characteristic Also, the theoretical characteristic 37 isnonlinear while the actual characteristic 36 is more nearly linear. Thecutoff value of the theoretical charn acteristic 3o, however, doesdefine the range in which actuai values of delay are observed.

Referring to FIG. 3 there is illustrated double-ended operation of thedevice of FlG. 1 whereby two of the transducers i7, 18, i9 and 20intercept the diffracted beam. in particular, an election is made tolaunch a beam from transducer f7 and intercept the ditfracted beam 'withtransducer Zti. ri`he distance separating transducers 1'? and is X, theangle of incidence of the beam on the grating 35 is i and the angle ofdiffraction of the diffracted beam is 9. With N, VL and f as before, theequai where i', is the distance from the transducer l to the point ofincidence on the grating 3S:

'where r2 is the distance from the transducer to the point ofdiffraction from the grating 35 Also,

.fl-5:13 sin 1142 sin (9) it is evident from Equations 7, 8 and 9parameters are completeiy specified whereby the delay time, td, betweenan input and output puise is uniquely determined by:

that the Referring to FIG. 5, characterisiics 38, 39, d@ show the delayfor different frequencies for separations, X, of 0.75, 1.25 and 1.50,respectively.

In fabricating the device of FIG. l, it is apparent that. thetransmitting and intercepting transducers need not both be placed on acommon side of the block iti. In fact, itcanwbe shown that increasedlinearity can be achieved by placing the transmitting and interceptingtransducers i7, i8, i9 or 20 on adjacent perpendicular sides with thegrating 35 disposed opposite the transuniting transducer 17, i3, il@ or26.

Referring to FIG. 6, there is shown a schematic rep resentation of anultransonic delay line Sti adapted to increase the frequency range or"operation by utilizing lenseless focusing. ln particular, the delay lineSi) includes a slab Sil of uniformly thick metal or other medium capableof propagating ultrasonic waves and generally having a circularconfiguration. Approximately one/sixth the circumference of the circularslab SIL is extended to the configuration of a Rowland circle here-1inafter'designated the Rowland circle portion 52 of slab Si. The Rowlandcircle portion 52 defines an arc of a radius equal to the diameter ofslab 51 and centered on the opposite circumference thereof. A grating 53is scribed transversely across the entire length of the Rovvland circleportion 52. In addition, indentations 51%, 55, Se, 57 having normalsdirected towards the center of IRowland circle portion 52 are disposedat uniform intervals around the slab Si, respectively, for somewhat lessthan half the circumference thereof commencing with the portion 52.

Transmitting transducers S8, 59, titi, 6i are disposed adjacent theindentations 5'4, SS, 56, 5'7, respectively. Lastly, a receivingtransducer 62 is disposed along the circumference of slab S1 for adistance substantially the same as the portion 52 and centered within aquadrant of slab 5l opposite the indentation 54. As before, thetransducers 53, 59, et), 6l, 62 may be of the PZT ceramic type.

Referring to FIG. 7, a Rowland concave grating is shown as are AOB, ie.,an arc of a circle on which a linear transverse grating has been ruled.A smaller circle with a radius of half the radius of arc AOB representsthe locus of converging points. Thus, as shown in FIG. 7, an inputaperture at C will be diifracted in phase across the curved surface atE, Oi, or F and be focused at the point D. FiG. 8 illustrates theacoustic equivalent of FIG. 7. Referring to FG. 8, a generator 6dprovides a signal input to transducer 5ft, 59, di) or dit whereby anuitrasonic wave is launched towards the ruled grating S35 within theacoustic transmission media or" slab 5i. The diracted wave isintercepted by the transducer 62 over a wide range of frequenciesthereby to provide a delayed signal at output terminals 6, o6.

What is claimed isi il. An ultrasonic delay line comprising means forprod viding a medium through which ultrasonic Waves may be propagated,said medium having first and remaining spaced surfaces, said firstsurface having the configuration of a Rowland circle; a grating disposedon said first surface of said medium, the lines of said grating beingnormal being normal to the curvature of said surface; a tirst transducerdisposed on one of said remaining spaced surfaces .,i of said medium forlaunching an ultrasonic wave corre- Viding a medium through whichultrasonic waves may be propagated, said medium having a first andremaining spaced surfaces; a single uniform reflecting grating disposedon said first surface of said medium, any cross section of said firstsurface of said medium taken normal to the lines of said single uniformgrating having the conguration of a Rowland circle; a first transducerdisposed on one of said remaining spaced surfaces of said medium forlaunching an ultrasonic -wave corresponding to an electrical impulse;and a second transducer disposed on said one of said remaining spacedsurfaces of said medium and spaced from said first transducer forintercepting said wave reected normally from the lines of said singleuniform reflecting grating thereby to delay said electrical impulse byan amount proportional to the distance traveled by said wave throughsaid medium.

References Cited UNITED STATES PATENTS Rankin S33-30 Mortley 333a-30Soller 333-30 Mason 333-30 Mortley S33-30 Papadakis 333-6 Auld 333-7HERMAN K. SAALBACH, Primary Examiner C. BARAFF, Assistant Examiner U.S.Cl. X.R.

